Lenticular Systems
The history of 3-D technology without glasses that reproduce scenes in motion essentially begins with F and H. Ives in the 1930's with the use of lenticules and film camera/projector arrays. The reproduction system suffered from parallax discontinuities, shallow depth of field and the need for multiple projection lamps.
In the 1940's, Ivanov, in Russia, demonstrated the radial raster stereoscreen constructed of about 3000 long conical lenses imposing very tight tolerances in implementation. Special visors had to be designed to help spectators locate the best view positions. The Russians admitted to the following problems: visual fatigue due to poor left and right eye separation and brightness differences; poor convergence and the appearance of “cardboard” images.
Lenticular 3-D displays use vertical elongated lenses (the height of the view screen) and selective vertical lines from several images. This approach suffers a loss of horizontal detail and is very susceptible to jitter demanding an extremely accurate scan.
Varifocal Mirror
The varifocal 3-D system used a rapidly vibrating reflective membrane to cause a flat image to move through a minimum depth and rapidly repeat. The system could not provide a detailed photographic-type image due to a severely limited image writing time constraint.
Barrier Strip
The barrier strip system used a “picket fence” array of vertical narrow slats running the height of the screen and having a narrow space between each slat. The slats were arranged near to and in front of the view screen so that observer's right and left eyes could not see the same areas of the view screen at the same time. Right and left scene information (in narrow vertical areas behind the slats) presented 3-D to eyes in special places. The system reduced the brightness and the horizontal resolution of the scene.
In France, F. Savoye demonstrated the “Cyclostereoscope” (a type of “barrier strip” system) by projecting two pictures through a very large revolving truncated drum of spaced slats onto an internal stationary reflective screen to a theater audience of 90 observers in the 1940's. Observers looked through the spaces between the revolving slats as the large drum of slats rotated. Observers had to stay within the tiring lateral confines of about 1.5 inches. The 3-D effect offered good resolution but with reduced brightness.
LCD Vertical Shutter
This type of 3-D display uses electronically controlled multiple narrow vertical LCD slats to selectively pass or block light. The elongated slats are arranged side by side in a vertical plane surface between a “bright” screen and the observer's eyes. The slats are a few inches in front of the screen. The concept requires a very bright screen due to the LCD slat aperture duty cycle and low throughput in the “on” mode. The images are usually only simple computer graphics figures due to the high scanning speeds required in this process. The concept is similar to the “Stereoptiplexer” of the 1970's except that conventional movies were captured by a horizontally moving relative motion camera/scene which generated 3-D movies without glasses by means of a fast moving “aerial” slit in a rotating mechanism. The advantage of the Stereoptiplexer over the LCD system was that a means was found to bring all of the light from the screen to the “aerial” slit and thus eliminate considerable light loss. The height of the aerial slit was several feet so a very wide vertical view angle was allowed. Pictures from standard 16 mm film arrived at the conventional speed of 24 frames per second but were projected internally in the system to 2000 frames per second by an internal scanner. The problem with the Stereoptiplexer was that the camera was constrained to look out only one side as it moved horizontally. The Stereoptiplexer was described in U.S. Pat. No. 4,089,597 dated May 16, 1978 and was invented by one of the inventors of the current patent application.
Flickering 3-D Methods
R. McElveen of South Carolina (an optometrist), has shown 3-D movies by alternating left and right eye pictures at low refresh rates but flicker was intolerable and the effects were difficult to sustain.
VISIDEP was another flickering 3-D system which was developed by three professors at the University of South Carolina. They used two cameras displaced vertically and then electronically switched between them at a 5 Hz rate. The effects were very poor and caused much eye strain.
LASER Activated Omni-View Wobble Plate
Texas Instrument's reflective disc attached at an angle to a motor shaft spinning at 10 r/s was selectively illuminated by one or more modulated LASER beams which were synchronized with the spin rate. The resultant image was confined to a minimum volume (about 4 inches in size). The image was viewable from any position in a hemisphere. The system was not compatible with TV signals but showed only simple graph shapes. The flicker is not tolerable unless the spin rate is about 6 times greater. Larger full color system would require multi-LASERS accurately located and timed and a disc spin rate of at least 60 r/s.
Holography
In the early 1980's Komar of Russia used the principle of holography to present 3-D pictures without glasses. Komar provided a special reflective holographic screen that worked like a multiple ellipsoid. The projector was at the common focus of the ellipsoids and there were as many ellipsoids as observers. Each ellipsoid had a second focus at the observer's eyes. It is reported that four exit pupils with a 3×4 foot monochrome picture was demonstrated. The exit pupils at each seat were about 10 inches wide and resembled invisible “port holds” through which an observer viewed the scene-image with camera/scene proximity. Seats had to be specially located.
MIT's Media Lab-Holographic Video
A holographic moving picture was presented by MIT's Media lab in 1990, containing a simple wire frame graphic image a few inches high and requiring the bandwidth equivalent of 160 television channels. The demonstration image had a low resolution of 64 lines and refreshed at 40 Hz providing a limited 15 degree view angle. The system only provided horizontal parallax which was done to limit the bandwidth. If a full color TV image (running at standard TV rates and having 24 bits/pixel) was shown on their system, the bit rate would be 36 trillion bits per second. In their system, light passes through a tellurium dioxide crystal (which must be the full size of a viewing screen in a practical system and was only a few inches in size at that time) where a varying voltage was translated into a varying phase of light beam to produce a hologram in motion.
3-D Systems Without Glasses During the Decade—1990 to 2000
Dimension Technologies built a transmissive high resolution display with a rear thin vertical light source to direct left and right eye information to a few people.
Infinity Multi Media built a high speed CRT with liquid crystal shutter and projection lens using a Fresnel lens to create several viewing zones. The system had a narrow view field. It was an electronic version of the mechanical Stereoptiplexer.
NYU used a retro reflective camera-based eye tracking system to scan the view area for left and right eyes and to direct, via a computer control, appropriate images to the eyes (presently for a single viewer but may be expanded).
DDD (Dynamic Digital Depth) can use multiple cameras or a single camera and synthesize data for the other eye via computer coded information or can scan a scene with a LASER range finder and apply to the final picture. 3-D results are good but from zoned areas of view only. They are reporting that 3-D without glasses can be geneated from any DVD movie. In this technology, the audience size is relatively small (i.e., it will not work for theater applications).
General Comments on the Above 3-D Systems Relative to Our Invention
All 3-D systems without glasses to date, suffer from various problems: minimum depth of field; constrained eye regions within the view area; flicker; high bandwidth; small image size; low brightness; poor resolution; tight equipment alignment tolerances; not compatible with standard motion picture software, video or standard TV; and difficult to scale up to theater size.
Our 3-D without glasses invention will provide: high brightness; high resolution; a deep depth of field without flicker; 3-D images to all members of a large audience (probably up to 500 people) without any special zoned areas of view. Also, not like the barrier systems, the head can be held in any position, even upside down and still perceive the 3-D effect as in nature. Our invention is directly compatible with existing movie software. The only limitation of our invention is in the need for relative horizontal motion between the camera and scene in any direction. The system will be described in detail in the Specification.